1. Field of the Invention
The present invention relates to a surgical instrument for crushing crystalline eye lenses by means of ultrasound, and for removing the lens debris by suction. A hollow needle is connected with an ultrasound generator received in a handpiece. The lumen of the needle is communicatively connected in terms of flow with a suction duct extending through the handpiece. The needle is surrounded by a sleeve made of plastic, forming a flow path communicatively connected in terms of flow with a feed duct of the handpiece for feeding rinsing liquid. This sleeve extends approximately along the entire length of the hollow needle, and has near its front end at least one outlet aperture for the rinsing liquid.
2. The Prior Art
Instruments useful for eye surgery are described in DE 40 08 594 A. Publications of Hans Geuder GmbH of Hertzstrasse 4, Heidelberg, Germany, relate to these instruments also.
In connection with such instruments, a needle forming an ultrasonic probe extends axially from a handpiece and is detachably screwed into a needle receptacle. This receptacle is designed like a sleeve and is longitudinally movable within the handpiece at high frequency, in a known manner.
The needle is a hollow needle with a lumen for removing by suction the rinsing liquid, and the lens debris carried along by this liquid. The lumen is connected with a suction conduit through a duct extending through the handpiece. The rinsing liquid is fed through a ring duct surrounding the end of the needle receptacle that is screwed onto the hollow needle.
When the instrument is used as intended, a plastic cap is exchangeably screwed onto the end of the handpiece at the needle end. This cap receives in a suitably dimensioned chamber, the end of the needle receptacle and a head of the hollow needle screwed to the receptacle. The plastic cap has a sleeve extending from the chamber, and surrounds the needle approximately along its entire length, forming a ring duct which is sealed at the front end of the sleeve, and which has lateral outlet apertures for rinsing liquid.
When the instrument is used, the hollow needle with the sleeve of the plastic cap surrounding it is inserted through an incision at the edge of the cornea into the anterior chamber of the eye which is to undergo the surgery. In a known manner, the lens is crushed by means of the hollow needle forming the ultrasonic probe. This is because the probe, which has a beveled segment at its end in most cases, focuses ultrasound into the lens. Rinsing liquid flows through the ring duct surrounding the needle receptacle, which is longitudinally movable at high frequency. The rinsing liquid then flows into the rear chamber of the plastic cap receiving the front end of the needle receptacle and the head of the needle screwed to the receptacle. Then the rinsing liquid flows via the ring duct between the hollow needle and the sleeve of the plastic cap surrounding the hollow needle. In this manner, rinsing liquid is supplied to the site of the surgery, and is then removed again by suction from the anterior chamber of the eye together with lens debris, via the lumen extending through the hollow needle.
Instruments of this type have been used successfully and, as a rule, permit without any problems the removal of lenses in cataract surgery. This is done by crushing the lens by means of ultrasound into very fine particles, and then by removing these particles by suction together with the rinsing liquid previously admitted into the anterior chamber of the eye. At the same time, the rinsing liquid flowing through the ring duct serves as a thermal insulation of the sleeve against the hollow needle, which heats up highly during the course of an operation.
It has been found that the sleeve, which in most cases consists of flexible material such as silicone, can be easily manipulated within the area of the wound. However, the sleeve may be constricted by the pressure applied by the edges of the wound, until this sleeve comes to rest against the hollow needle. This may lead to local heating of the sleeve, and in extreme cases, it may even lead to strangulation of the ring duct. In connection with this ring duct strangulation, it may lead to overheating of the entire area between the site of the constriction and the needle point. This consequently leads to damage to the surrounding eye tissue caused by heat, and particularly to the edges of the wound enclosing the sleeve.
In order to avoid such damage, a hollow needle has been described in trade publication "CATARACT/IOL", which has radially outwardly projecting longitudinal ribs on which the sleeve surrounding the hollow needle supports itself radially if constrictions occur. With this state of the prior art, it is assured that feed ducts for the rinsing liquid are kept open with a high degree of probability. However, at the site of any constriction, the sleeve is in direct contact with the ribs of the hollow needle. Such contact areas may cause undesirable heat transfer from the hollow needle, which consists of metal, and which consequently has good thermal conductivity, to the sleeve, and to the eye tissue resting against the outside of the sleeve.